1. Field of the Invention
The present invention relates to a mechanism for monitoring a voltage-stacked system, and more particularly, to a mechanism of a voltage-stacked system capable of utilizing a plurality of monitoring circuits to manage a plurality of stacked voltage sources coupled in series.
2. Description of the Prior Art
With the trend that the portable electronic devices are designed in small sizes, the portable electronic devices such as the personal digital assistant (PDA), digital camera, portable audio/video (AV) player, notebook and tablet are becoming more and more popular. To achieve portability, these portable electronic devices mainly utilize the batteries as their power sources. When the electricity of a battery device is depleted, it can be charged by a dedicated charger or by directly connecting to an alternative current (AC) voltage source. Due to the limited voltage level and electric capacity of a single battery, in some occasions, many batteries are combined to form a voltage-stacked device such as a battery set to provide higher voltage and more electric capacity.
The battery set can be charged and discharged many times till its service life ends. The service life of a battery set depends on the physical characteristic and charging mode of the batteries in the battery set. In general, when larger charging voltage/current is used, the charging period is shorter. But, larger charging voltage/current might reduce the service life of the battery. Hence, although over-discharging or over-charging can increase the capacity of the battery, the service life of the battery would be shortened.
Due to the manufacturing errors, the characteristic and aging rate of each battery of the battery set might be different from one another. A battery having greater capacity tends to be under a light charging/light discharging state, and a battery having smaller capacity tends to be under an over charging/over discharging state. If each of the batteries has a different level of charging/discharging state in a long term, the difference of the characteristics possessed by the batteries will be more obvious. Although the batteries with larger capacity can be still functional under the condition where the batteries with smaller capacity fail earlier, the overall performance and service life of the battery set will decrease rapidly. Hence, there is a need to individually monitor each battery to prevent it from being over-charged/over-discharged or damaged.
The monitoring circuit of the voltage system is usually implemented with integrated circuits. However, the voltage rating of an integrated circuit chip is limited. When a voltage-stacked system with a high total voltage is to be monitored, multiple integrated circuit chips can be used to monitor serially-coupled voltage sources in such a way that the voltage endured by each integrated circuit chip is reduced. However, such monitoring structure causes the ground voltage levels of the chips to be different. When one chip needs to collect the monitoring information from other chips, the communication link connected therebetween are generally implemented using expensive optical coupling elements or complicate voltage level shifting circuits.
Hence, there is a need to provide a simple communication circuit and mechanism to collect the monitoring data of the voltage-stacked device to facilitate intelligent management to increase the efficiency and service life of the voltage-stacked device.